Paying for one cruise is an achievement for many clients. Imagine being charged twice for the same cruise booking?

But that’s what happened to some customers of Cunard, P&O Cruises and Princess Cruises late last week when their bank cards were debited a second time. Some guests have written publicly on CruiseCritic.com's consumer forums that the second billing -- for some, a charge that amounts to thousands of U.S. dollars or U.K. pounds -- has overdrafted their bank accounts.

“We are aware there has been an error within our payment system where balances have been recharged and are showing as ‘pending’ on the statements of a number of guests,” Jackie Chase, director of public relations for North America, Cunard Line, told Travel Agent on Sunday.

Chase also stressed that “we would like to sincerely apologize and reassure our guests that we are working as fast as possible on a resolution.”

Then later in the same day, Chase provided this updated statement:

"On Friday we were made aware of a one-off technical error made by Elavon, our third party payment processor, in relation to card payments for cruise bookings with Cunard, P&O Cruises and Princess Cruises.

"Refunds are already being processed and we are working with Elavon at the highest level to investigate how this happened and to ensure that this could not happen again.

"Any charges incurred by guests as a result of this issue will be refunded. Once again we apologize to those guests who were affected by this error." Chase said the refunds would be handled by Elavon.

On CruiseCritic.com's consumer forums over the weekend, one cruiser, "maximusas," publicly said she happened to look at her credit card, and on two credit cards previously paid with Princess, pending transactions are showing to take more than £500 between the two cards.

The writer contacted the line: "Told me to phone my bank too but assured me they would refund it if it came off. Phoned the bank and they said until it fully debits then they can't do anything. Double check your credit cards."

Another bulletin board writer said that P&O took 3,600 UK pounds out of his bank account Friday, and he'd already paid for the cruise earlier in the year, so "now I am overdrawn in my bank..."

On Saturday, The Mirror, a UK publication, reported that that Cunard learned of the issue when customers complained about the double payment.

Travel Agent also reached out to Princess Cruises for comment, and is awaiting that line's statement. We'll post it here when it's received. P&O is primarily a U.K. sourced brand.